Floating roof tanks are conventionally used to hold or store liquid mixtures which give off gaseous vapors. The roof of such tanks actually floats on the liquid thereby keeping gases from evaporating out of the liquid mixture. A floating roof tank can have a fixed roof above the floating roof. In the case of a sour water liquid mixture, such as a processing liquid in the petroleum industry, the sour water mixture may contain hydrogen sulfide gas and/or other noxious gases. Such sour water is stored in floating roof tanks in order to keep the toxic hydrogen sulfide vapors intermixed with the water. Such sour water, however, contains light hydrocarbons such as NAPHTHA. It is desirable to separate out the light hydrocarbons not only to retrieve the valuable hydrocarbons but also to permit the sour water to be processed. The light hydrocarbons separate out naturally and the skimmer removes them from the surface of the water.
The present invention, in its preferred embodiment, sets forth a skimmer being capable of attachment to the underside of conventional floating roofs for removing the light hydrocarbons from the tank without interfering with the operation of the floating roof tank. Other applications for using the skimmer of the present invention to separate a lesser specific gravity immiscible liquid from a mixture of two immiscible liquids can be made.
A patentability investigation conducted on the invention resulted in the following U.S. patents:
______________________________________ U.S. PAT. NO. INVENTOR DATE ______________________________________ 3,535,236 Travis, H. J. October 20, 1970 3,628,660 Cornelis In't Veld Dec. 21, 1971 4,082,669 Bainbridge April 4, 1978 4,111,806 Wright et al Sept. 5, 1978 4,132,645 Bottomley et al January 2, 1979 4,147,629 Geurtsen April 3, 1979 ______________________________________
The 1979 patent issued to Bottomley et al. (U.S. Pat. No. 4,132,645) sets forth a two stage oil separator for skimming hydrocarbons from a hydrocarbon-water mixture. The disclosed separator utilizes three hollow cylindrical floats supported on the mixture. A funnel-shaped skimmer having perforations located around the top of the funnel is disposed in the center of the three floats and can be adjusted vertically. Through proper adjustment, the funnel can be positioned in the mixture so that the lighter hydrocarbons which float on the mixture can be skimmed off into the funnel and downwardly through an interconnecting hose to a point remote from the storage tank.
The 1971 patent issued to Veld (U.S. Pat. No. 3,628,660) sets forth a separator for immiscible liquids such as oil and water and comprises a bell-shaped float. The 1978 patent issued to Wright et al. (U.S. Pat. No. 4,111,806) sets forth a dome or diaphragm which is also designed to float upwardly in the presence of more dense liquid and below in the presence of less dense liquid. The Wright et al patent represents an improvement of the Veld approach. In both approaches, the lighter oil collects within the bell causing the bell to rise to the top of the separation tank. When the bell reaches a given height, the accumulated oil exits the chamber through an outlet port causing the bell to drop back to its initial level. The separation cycle then begins anew as additional oil-water mixture is allowed to enter the system. The 1979 patent issued to Geurtsen (U.S. Pat. No. 4,147,629) sets forth an approach similar to Veld and Wright.
The 1978 patent issued to Bainbridge (U.S. Pat. No. 4,082,669) utilizes three separating stages for separating oil from water. The first stage utilizes a series of plates over which the mixture flows in an upward direction so that oil gathers on the upper surfaces of the plates. In the second stage, a coagulator is utilized through which water and any oil not separated in the first stage flows in an upward direction wherein the coagulator bed comprises finely divided material having a greater affinity for oil than water. Finally, in the third stage, a screen is utilized which is fine enough to remove water and leaving any second stage oil of molecular fineness to be collected.
Finally, the 1970 patent issued to Travis (U.S. Pat. No. 3,535,236) sets forth a floating cover for a liquid holding tank for use in covering gas-liberating digesters which are used to treat sewage solids.
None of the prior art approaches found in the patentability search set forth or even suggest the teachings of the present invention for utilizing a light hydrocarbon skimmer actually incorporated into the roof of a sour water storage tank.